Mobile telephones systems rely on radio waves to provide communication between the fixed wire network and the mobile station (MS). Base Stations (BS) are geographically fixed radio frequency transmitters and receivers that provide the radio wave communication between the network and the individual mobile station. Each base station is limited by power requirements and frequency availability to the size of the geographical area that can be covered by each base station.
Thus, a system of adjacent cells, each having a base station transmitter-receiver has been developed. The cells are clustered into groups that are controlled by mobile service switching centers (MSC) that function to provide communication between the cell cluster associated with the particular MSC and the remainder of the network. Clusters are typically comprised of four, seven or twelve cells, however, many cell clusters of other numbers of cells exist. To a great extent, the cell cluster size is influenced by the number of base stations that can provide a manageable paging function. In effect, every base station in the cell cluster simultaneously page a particular mobile station when a call is placed from the network to that mobile station. The cell clusters are commonly referred to as mobile location areas (MLA) or Local Areas (LA).
Each mobile station must be identifiable for billing, network connection and paging purposes. Therefore, registers are provided in the network to serve as the repository of the identification information needed for each mobile station.
Each MLA is controlled by a MSC that has a Home Location Register (HLR) and a Visitor Location Register (VLR) associated with it; the HLR providing a register for mobile stations that are assigned to that particular cluster and the VLR providing a register for mobile stations as the mobile station travels into the MLA.
Further, each mobile station is provided with means to continuously determine if it is located in its home MLA. When the mobile station moves from its home MLA to another MLA it must register in the VLR of the MLA in which it is physically located. The main disadvantage of registering in a MLA as a visitor is the diversion of the base station transceiver to registration usage rather than network transmission capacity. Thus, minimizing the use of a base station digital control channel for signalling traffic will result in the availability of more bandwidth which can be transformed into communication services.